1. Field of the Invention
This invention relates to junction for medical instruments, and more particular to a junction for tubular members in medical instruments made of polyvinyl chloride such as blood bags and transfusion solution bags.
2. Description of the Prior Art
Heretofore, medical instruments such as blood bags and transfusion bags have been mostly made of polyvinyl chloride by reason of high fabricability, physiological safety, high transparency, low price and the like. They are provided at various portions thereof with tubular members. Proper junction of these tubular members is necessary for such instruments. In the case of a blood bag of one type, for example, one blood collection bag has connected thereto a blood collection tube which is connected to a hub having a blood collection needle fastened to the leading end thereof. A blood bag of another type comprises at least one auxiliary bag besides the aforementioned blood collection bag fitted with a blood collection needle, a hub and a blood collection tube. The auxiliary bags themselves as well as the auxiliary bag and the blood collection bag are interconnected through connection tubes with the aid of a manifold.
The joining members used for the blood collection tube, between the blood collection tube and the manifold, and between the connection tubes and the manifold, for example, are relatively thin, long tubes. Since they are too thin to admit a core wire, their union by high-frequency heating has so far been impractical. The union of two such tubular members, therefore, has heretofore been accomplished by applying a solvent such as, for example, tetrahydrofuran (THF) which is capable of dissolving vinyl chloride polymers, to the ends of the tubular members to be joined thereby partially dissolving the ends, and thereafter fitting one of the dissolved ends into the other, for example. Another method of effecting the union of such tubular members is carried out by inserting one of the ends of the tubular members not yet treated with the solvent into the other, applying the aforementioned organic solvent to a fine gap between the joined ends thereby allowing the applied solvent to seep through the annular interface of the joined ends by capillary action and induce partial dissolution of the joined ends and thereafter causing the partially dissolved ends to fuse with each other and resolidify.
The method which employs an organic solvent has the disadvantage that sufficient seepage of the organic solvent through the interface and, consequently, thorough union of the joined ends of the tubular members is not obtained when the aforementioned gap is too small. If excess solvent is used and the gap is too large, the solvent can flow out of the joined ends. In the case of a blood bag already containing an anticoagulant or a transfusion bag containing a medicinal solution for transfusion, for example, the excess solvent may find its way into the solution in the bag. The use of the organic solvent has the disadvantage that the joined ends tend to undergo blushing or gradual degradation and the organic solvent itself, because of its high volatility, tends to jeopardize the manufacturing facility and inflict cracks on molded articles of polyvinyl chloride.